It is generally known to a person skilled in the art in the field of rolling bearing technology that shafts or hubs with axial and radial torque loading are usually supported by means of angular contact rolling bearings which, on account of the high loading, are generally formed as two tapered-roller bearings which are inclined with respect to one another and pre-stressed in the axial direction. Said tapered-roller bearings are formed with a large pressure angle in the case of high axial forces and ensure a high level of stiffness of the supported shaft. For optimum bearing kinematics, said tapered-roller bearings are designed structurally such that the longitudinal axis of the tapered rollers is arranged fundamentally at right angles to the respective pressure angle axis, and the cone angle of the tapered rollers and the angle of inclination of the raceways in the bearing rings are dimensioned such that a conical envelope which encompasses the tapered rollers is arranged with its cone tip precisely on that point of the bearing longitudinal axis at which the tapered-roller longitudinal axis also intersects the bearing longitudinal axis. This has the effect that both the tapered rollers and also their raceways are subjected to uniform loading over their entire width.
However, since tapered-roller bearings of said type experience sliding friction between the end surface of the tapered rollers and the guide surface of the bearing rim on account of their preload, as a result of which sliding friction wear occurs on the tapered rollers and on the bearing rim, it has been proposed in DE 198 39 481 A1 to replace the tapered-roller bearings with two-row tandem angular contact ball bearings which can be loaded from one side and which are inclined in an O-arrangement with respect to one another. Said tandem angular contact ball bearings are composed substantially of an outer bearing ring and an inner bearing ring and of a plurality of bearing balls which are arranged between the bearing rings and which are arranged in two rows with different pitch circle diameters adjacent to one another and offset in height and which are held at uniform intervals with respect to one another in the circumferential direction by means of two separate bearing cages for each row. The inner side of the outer bearing ring is formed here with two adjacent groove-shaped raceways which are arranged on common pressure angle axes with two likewise adjacent groove-shaped raceways in the outer side of the inner bearing ring. In each case one row of the bearing balls rolls with their running surfaces on said raceways, with the bearing balls of the row with the larger pitch circle diameter having a greater diameter than the bearing balls of the row with the smaller pitch circle diameter. By using tandem angular contact ball bearings of said type instead of tapered-roller bearings, it is intended here to obtain a significantly reduced friction torque on account of the now eliminated sliding friction between the bearing balls and the raceway shoulders, as a result of which the wear and the temperature of the bearing are reduced and its efficiency is improved.
Such a replacement of tapered-roller bearings with double-row tandem angular contact ball bearings has nevertheless proven to be disadvantageous in practice because said tandem angular contact ball bearings require an increased axial installation space on account of the raceways for the bearing balls being arranged adjacent to one another and on account of the large diameter of the bearing balls in relation to tapered-roller bearings in order to obtain the required load rating. Furthermore, if it is necessary for a tandem angular contact ball bearing of said type to have an even higher load rating than a tapered-roller bearing, complex alterations to the bearing seats are therefore necessary which disadvantageously increase the production costs of the respective component. Furthermore, double-row tandem angular contact ball bearings of said type also entail increased production and material expenditure in relation to tapered-roller bearings during bearing production not least on account of the necessary use of two bearing cages, and therefore the production costs of said double-row tandem angular contact ball bearings are likewise increased. Tandem angular contact ball bearings of said type have also proven to be sub-optimal with regard to bearing kinematics, since the large bearing balls of the two rows which are used result in a conical envelope, which makes contact at a tangent with their diameters, whose cone tip deviates considerably from the point of intersection of the transverse axis, which is at right angles to the pressure angle axis, of two adjacent balls with the bearing longitudinal axis.
To avoid said disadvantages, it has therefore been proposed by the German patent application with the file reference 10 2005 014 556.6, which was not yet published on the filing date of the present patent application, in a double-row angular contact rolling bearing, for the rolling bodies of each row to be formed not as bearing balls but rather as spherical rollers with in each case two side surfaces which are flattened symmetrically from a spherical basic shape and which are arranged parallel to one another, and for two rows with different pitch circle diameters to be arranged adjacent to one another and offset in height, similarly to tandem angular contact ball bearings. Here, the spherical rollers of the row on the larger pitch circle again have, in their spherical basic shape, a larger diameter than the spherical rollers of the row on the smaller pitch circle, and the spherical rollers of the two rows roll with their running surfaces in each case two adjacent groove-shaped raceways in the outer bearing ring and in the inner bearing ring. Here, the raceways of the spherical rollers have pressure angle axes running parallel to one another and are arranged so as to adjoin one another in such a way that the in each case adjacent spherical rollers of each row are arranged directly adjacent to one another with their side surfaces which point toward one another, and guide one another. By using spherical rollers as rolling bodies, it is the intention to distinguish an angular contact rolling bearing of said type from multi-row angular contact ball bearings primarily by a minimized axial and radial installation space, and by an identical or increased load capacity and by the possibility of using a single-part bearing cage for the two rows, while maintaining similar production costs.
However, it has proven to be disadvantageous that the proposed spherical-roller bearing is likewise not yet of optimal design with regard to bearing kinematics, since, as can be clearly seen from FIG. 2 of the patent application, the common transverse axis of in each case two adjacent spherical rollers does not run at right angles to the pressure angle axes of the spherical rollers. A conical envelope which makes contact at a tangent with the two spherical roller diameters would therefore duly lie with its cone tip on the bearing longitudinal axis but would nevertheless deviate horizontally to a considerable extent from the point of intersection of a transverse axis, which runs at right angles to the pressure angle axis, of the two spherical rollers with the bearing longitudinal axis. Here, the oblique alignment of the actual transverse axis of the two adjacent spherical rollers causes those side surfaces of the spherical rollers which point toward one another, and the rotational axes of the spherical rollers, to have a radial offset with respect to one another, as a result of which the spherical rollers do not roll synchronously with respect to one another during bearing operation. This firstly results in friction between the individual spherical roller pairs, and secondly, the bearing cage, as it guides the spherical rollers, is subjected to such a high loading that increased heat is generated and the rolling bodies and bearing cage are subjected to increased wear, and the bearing therefore fails prematurely.